Providing adequate illumination in hazardous work areas, particularly explosive or flammable work areas, has been difficult to accomplish with adequate safety. Most lighting systems utilize circuitry with an inherent spark potential, operate at high temperature, or both. In addition, large area or long-length lighting systems commonly require power inputs which create the hazard of fire or explosion in these unique environments. This is true for both ambient lighting and emergency lighting. While daylight operation can be an adequate answer to the former, emergency lighting must operate at all times and in adverse atmospheres (smoke, fog, etc.), and hence creates special difficulties.
Certain metering and other devices for use in hazardous areas have used what is commonly known as "intrinsically safe" ("IS") circuitry and equipment, where low power input is adequate, such as about one watt or less. IS systems call for the use of low capacitance, current and voltage for safety reasons. Components and circuitry of this type are provided, for example, by the MTL Group of Luton, England, but such systems have not been favored for use in lighting systems as acceptable light sources were not available.
EL lights have been used for exit path marking systems, such as those provided by Loctite Luminescent Systems, Inc., Lebanon, N.H., U.S.A. Generally, such EL lights and EL systems require the use of high capacitance and voltage in order to provide adequate brightness and sufficient illumination of an area for effectiveness. Thus, such EL lights and EL systems have not been used in, nor were they believed to be suitable for, hazardous environments where the potential for explosions due to electrical sparks or high temperatures has existed.